High metabolic activity in the dorsal vagal complex of Brattleboro rats

Receptor densities for angiotensin II and atriopeptin are particularly high in the dorsal vagal complex (DVC) of the caudal medulla oblongata. Measurements of glucose metabolism in individual components of the DVC, compared with those in Long-Evans rats, revealed that the area postrema was activated selectively both in water-sated and water-deprived Brattleboro rats, which have high circulating levels of angiotensin II. Other parts of the DVC, including subnuclei of the nucleus of the solitary tract and the dorsal motor nucleus of the vagus nerve, as well as brainstem structures within efferent trajectories of the DVC, had elevated rates of glucose metabolism in Brattleboro rats deprived of water overnight and in Sprague-Dawley rats dehydrated for 120 h. The findings are consistent with neural activation by angiotensin II, as either a hormone or neurotransmitter, within subregions of the dorsal medulla oblongata having high densities of putative receptors and immunoreactive perikarya and fibers containing both angiotensin II and atriopeptin.

Effect of antidiuretic hormone on renal organic osmolytes in Brattleboro rats

Homozygous Brattleboro rats were used to study the effect of antidiuretic hormone (ADH) on organic osmolytes, which have been shown to be involved in the cellular osmoadaptation in renal inner medulla. With the use of enzymatic spectrophotometric methods, glycerophosphorylcholine, sorbitol, and inositol were determined in kidney sections from papillary tip (IM3) to cortex. Compared with normal rat kidneys, IM3 of untreated Brattleboro rats (urine osmolality 132 mosmol/kg) were sorbitol depleted (16 +/- 1 vs. 371 +/- 37 mumol/g protein) and glycerophosphorylcholine was reduced to 20% (131 +/- 16 vs. 658 +/- 52 mumol/g protein). In contrast inositol was not changed (147 +/- 25 vs. 177 +/- 29 mumol/g protein). Similar effects were obtained in all medullary sections. Continuous treatment with ADH increased urine osmolality already after 5 h but renal glycerophosphorylcholine and sorbitol content only after 24 h. Normal osmolyte levels were reached after 3 days of ADH treatment when urine osmolality was 1,595 mosmol/kg. Inositol did not exhibit comparable changes during ADH treatment. The present results indicate that ADH, possibly by increasing interstitial tonicity, leads to increased glycerophosphorylcholine and sorbitol, but not inositol, contents.

Plasma lipid secretion and clearance in hyperlipidemic JCR:LA-corpulent rats

The JCR:LA-corpulent rat is an obese, hyperlipidemic, hyperinsulinemic strain that is atherosclerosis-prone and develops myocardial lesions. The hyperlipidemia is due to elevated plasma levels of a large relatively triglyceride-rich very low density lipoprotein (VLDL). Both corpulent and lean male and female rats were studied. Postheparin lipid clearance and apparent hepatic secretion rate after Triton WR1339 inhibition of lipoprotein lipase were determined. The concentrations of cholesterol and cholesteryl esters were not significantly altered by either treatment. Triglycerides showed rapid postheparin clearance in corpulent rats. The apparent hepatic secretion rate was markedly higher in corpulent male rats than in lean male rats, and the rate in corpulent females was again higher, reflecting the higher serum triglyceride concentrations in corpulent female rats. The relative secretion rate of C:48 triglyceride molecular species was lower than that of the C:50 to C:56 species, while the postheparin clearance of C:48 triglyceride molecular species was impaired compared to the C:50 species and those with higher carbon numbers. This effect was more marked in the male than in the female corpulent rats. The results indicate that VLDL hyperlipidemia in the corpulent rat is due to hepatic hypersecretion of VLDL and not to a defect in lipoprotein lipase. Further, the atherogenesis that is characteristic of the corpulent male rat may be related to the differential metabolism of fatty acids.

Lack of effect of vasopressin replacement on renin hypersecretion in Brattleboro rats

To determine how the vasopressin deficiency in homozygous Brattleboro rats with diabetes insipidus produces increased renin secretion, homozygous and heterozygous Brattleboro rats were infused through subcutaneously implanted Alzet minipumps for 1 wk with a dose of arginine vasopressin that restored plasma vasopressin to normal in the homozygous animals. In the homozygous animals, plasma renin activity (PRA) and the PRA response to immobilization remained elevated compared with Long-Evans controls. Propranolol reduced PRA to normal and markedly reduced the PRA response to immobilization. PRA was normal in heterozygous Brattleboro rats. The data indicate that the increased renin secretion in homozygous rats is a result of increased sympathetic activity, and because circulating vasopressin does not cross the blood-brain barrier, it seems likely that the increased sympathetic activity is central in origin.

An explanation for decreased ketogenesis in the liver of the obese Zucker rat

These studies were undertaken to further characterize and explain the differences in hepatic fatty acid metabolism between lean and obese Zucker rats. It was shown that the rate of palmitate or octanoate oxidation and the inhibition of palmitate oxidation by malonyl CoA in mitochondria isolated from lean and obese Zucker rats were similar. Cytochrome oxidase activity was similar in lean and obese rat livers. It was found that the addition of cytosol from the obese rat liver inhibited palmitate oxidation by 20-30% in mitochondria isolated from lean or obese rat livers and thus reproduced the conditions observed in the intact cell. Increased concentrations of metabolites such as malonyl CoA and glycerophosphate in the liver of the obese rat are likely contributors to this inhibitory effect. These results are extrapolated to the intact cell and suggest that decreased hepatic fatty acid oxidation in the obese rat can be accounted for by cytosolic influences on the mitochondria. The decreased rate of fatty acid oxidation observed in the intact hepatocyte or perfused liver cannot be explained by a defect in the capacity of mitochondria to oxidize substrate or by a decrease in mitochondrial number in the obese rat liver.

In vitro and in vivo growth hormone responsiveness to growth hormone-releasing factor in male and female Zucker rats

In order to determine whether there is an anomaly in the pituitary responsiveness to growth hormone (GH)-releasing factor in the genetically obese rat, we examined the in vitro and in vivo effects of rGRF(1-29)NH2 (GRF) on GH release in male and female Zucker rats. The effect of increasing GRF concentrations (1.56, 6.25, 12.5 25 and 50 pM) was first tested on GH release from freshly perifused anterior pituitary cells. In both sexes, the GH response per one pituitary equivalent to each GRF concentration tested was reduced in the obese group. However, when GH release was expressed as a percent of initial cell GH content, there was no difference between the lean and the obese groups. Furthermore, under pentobarbital anesthesia, GRF was injected intravenously at two consecutive doses of 0.8 and 4.0 microgram/kg body weight in obese and lean animals. In both sexes, the GH response to each dose of GRF tested was decreased in the obese group. Basal serum GH concentrations were similar in male and female obese rats compared to their respective lean siblings. In conclusion, this study demonstrates a decrease of the in vitro and in vivo pituitary response to GRF in the obese Zucker rat, suggesting a possible secondary defect at the pituitary level.

Abnormal fatty acid utilization by cultured cardiac cells from 7-day-old obese Zucker rats

Fatty acid utilization by muscle and nonmuscle heart cells in culture has been investigated in the 7-day-old Zucker rat to determine if this tissue could contribute to the lower energy expenditure reported in obese rats at the onset of obesity. The partitioning of oleate to oxidation and esterification products and the effect of genotype on this partitioning according to cell types were studied. Results showed that the fatty acid beta-oxidation and its esterification in neutral lipid was decreased by 30% in beating muscle cells from obese animals when compared with those from lean animals. In contrast, nonmuscle cells exhibited a decreased beta-oxidation alone. A similar fatty acid composition of the phospholipids was found in non-muscle cells of obese animals and their lean litter mates. In muscle cultures, palmitic and oleic acids are lower in cells of obese rats than in those of lean rats. The present study indicates that a defect in energy metabolism could be found in heart cells at the onset of obesity, suggesting that this defect is determined by intrinisic factor(s).

Neuropeptide Y (NPY) and vasopressin (AVP) in the hypothalamo-neurohypophysial axis of salt-loaded or Brattleboro rats

A close anatomical relationship between nerve terminals containing neuropeptide Y (NPY) and vasopressin (AVP) has been demonstrated in the hypothalamic paraventricular (PVN) and supraoptic nuclei (SON). Furthermore, injections of NPY into the SON increased plasma concentrations of AVP in the rat. These data suggest a potential involvement of hypothalamic NPY in fluid homeostasis in the rat. Therefore, we have studied the effect of elevated plasma osmolality on the concentration of NPY and AVP in the hypothalamus and neurointermediate lobe (NIL) of the pituitary gland. Furthermore, we measured the concentration of NPY in the AVP-deficient Brattleboro rat, which suffers from diabetes insipidus and hyperosmolality. Salt-loading increased plasma osmolality and the concentration of AVP from 2.0 +/- 0.5 to 4.1 +/- 0.6 pg/ml after 7 days. The concentration of NPY in the NIL doubled after 7 days of salt-loading, from 7.9 +/- 0.6 ng/mg protein to 15.2 +/- 1.4 ng/mg protein, whereas AVP concentrations fell from 2285.7 +/- 210.9 ng/mg protein to 187.5 +/- 2.5 ng/mg protein. AVP concentrations in the ME increased transiently after 2 days of salt-loading and returned to control levels after 7 days. In contrast, NPY concentrations in the ME were unchanged at 2 days and were increased 61% after 7 days. NPY concentrations also were significantly elevated after 7 days of salt-loading in the preoptic area (POA) and mediobasal hypothalamus (MBH). The concentration of NPY in the NIL of the homozygous Brattleboro rat was 2-fold greater than in the heterozygous Brattleboro rat and 4-fold greater than in Sprague-Dawley rats used as controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between increased binding and insulin-like effects of human growth hormone in adipocytes from young fa/fa rats

Binding and insulin-like effects of human GH (hGH) in inguinal adipocytes from young lean Fa/fa and obese fa/fa Zucker rats were studied. The binding of [125I]hGH per unit surface area is 2-fold higher in adipocytes prepared from 16- and 30-day-old fa/fa rats than in cells from lean littermates. A 3-h preincubation of the cells increases the hGH-binding capacity without changing the affinity of the binding, regardless of genotype. Freshly isolated adipocytes from 30-day-old lean rats fail to respond to hGH, whereas after preincubation of the cells, hGH produces a maximal 105% increase in glucose transport and a maximal 40% increase in glucose oxidation. In contrast, freshly isolated adipose cells from fa/fa rats are already responsive to hGH and the amplitude of the response is markedly elevated in preincubated cells, with a 430% stimulation of glucose transport. The concentration of hGH (1 nM) that inhibits 50% of [125I]hGH binding and that which produces half-maximal stimulation of glucose transport as well as glucose metabolism are not different, suggesting the absence of spare receptors for these insulin-like effects of hGH. Plots of GH effects on glucose transport as a function of receptor occupancy are linear, with a change in the slope after preincubation. Our results suggest a strong correlation between binding of hGH and actions on glucose transport and glucose metabolism in adipocytes of young Zucker rats.

Atrial natriuretic peptide in plasma, atria, ventricles, and hypothalamus of Long-Evans and vasopressin-deficient Brattleboro rats

To evaluate the role of vasopressin in the regulation of atrial natriuretic peptide (ANP) secretion, the plasma, atrial, ventricular, and hypothalamic levels of ANP were measured in Long-Evans (LE) and vasopressin-deficient Brattleboro (DI) rats. Total atrial immunoreactive ANP (IR-ANP) as well as right auricular IR-ANP concentration were higher in the DI than in the LE rats, whereas no significant difference was noted in left auricular IR-ANP concentration. In the left ventricle of DI rats, the IR-ANP concentration was 82% greater than that in the LE rats, while no substantial difference was found in the right ventricular IR-ANP concentration between the strains. Normal LE rats had low levels of left ventricular ANP mRNA and barely detectable ANP mRNA in the right ventricle, DI rats showed a 3-fold greater ANP mRNA concentration in the left ventricle than age-matched LE controls, and ANP mRNA levels were also increased in the left auricle of DI rats. The hypothalamic IR-ANP content, but not the concentration, was significantly increased in the DI compared to the LE rats. Despite increased cardiac IR-ANP and ANP mRNA levels, plasma IR-ANP concentrations were similar in the conscious DI rats (97 +/- 9 pg/ml; n = 13) and the LE rats (95 +/- 8 pg/ml; n = 15). Volume expansion (1.1 ml/100 g BW of 0.9% saline, iv) increased right atrial pressure and caused a significant rise in plasma IR-ANP in both strains (P less than 0.01). Elevations of plasma IR-ANP concentrations caused by volume loading were comparable in LE and DI rats in either the absence or presence of exogenous vasopressin (5 ng/kg.min, iv), which, when infused alone, did not significantly influence the plasma IR-ANP concentration. However, the relation between the change in IR-ANP concentration and the change in right atrial pressure shifted to the left, and thus, for a given increase in right atrial pressure, a greater amount of IR-ANP was released in the vasopressin-treated rats than in the control animals. These results demonstrate that although acute volume expansion does not necessarily require endogenous vasopressin for the ANP secretory response, vasopressin increased the ability of volume expansion to induce ANP release, thus modulating the direct mechanical stimulus-induced ANP secretion. The increased left ventricular levels of immunoreactive ANP and augmentation of ANP mRNA levels in Brattleboro rats despite normal left ventricular weight to body weight ratio show that increased ANP gene expression may occur in the ventricles independently of hypertrophy.

Organic osmolytes in inner medulla of Brattleboro rat: effects of ADH and dehydration

Inner medullary methylamine [glycerophosphorylcholine (GPC) and glycine betaine (betaine)] and polyol [sorbitol and myo-inositol (inositol)] osmolytes were measured in water-restricted and antidiuretic hormone (ADH)-infused Brattleboro (DI) rats. Compared with DI rats allowed water ad libitum, rats dehydrated for 3 days had higher urinary osmolality (Uosmol) (812 vs. 239 mosmol/kgH2O) and plasma osmolality (Posmol) (333 vs. 296 mosmol/kgH2O). Dehydration reduced betaine content (36 vs. 66 nmol/mg protein) but had no significant effect on GPC, sorbitol, or inositol. In separate protocols, DI rats, allowed water ad libitum, were infused for either 3 or 12 days with either ADH in saline (+ADH) or saline alone (-ADH). Compared with -ADH controls, 3- or 12-day ADH-infused rats were antidiuretic (Uosmol, 1,000-1,300 mosmol/kgH2O) but not dehydrated (Posmol, 297-300 mosmol/kgH2O). Three days of ADH infusion caused an increase in GPC (340%), betaine (80%), and sorbitol (248%) but not in inositol. After 12 days of ADH, further increases were observed in GPC (730%) and sorbitol (870%); inositol was also elevated (170%), whereas betaine was unchanged. Consequently, the total osmolyte content was significantly higher in +ADH than in -ADH [449 vs. 256 (3 days) and 778 vs. 199 (12 day) nmol/mg protein], whereas total osmolyte levels in dehydrated and control rats were similar (222 vs. 219 nmol/mg protein).(ABSTRACT TRUNCATED AT 250 WORDS)

Activity of hepatic glucose phosphorylating and NADPH generating enzymes in Zucker rats

The activities of hepatic enzymes involved in glucose phosphorylation and NADPH production were studied in male and female obese Zucker rats (fa/fa) and lean control animals (Fa/-). The fa/fa animals were heavier and had higher serum insulin levels than the lean rats. The glucokinase activity and the total glucose phosphorylation capacity were also higher in the obese animals. The activity of glucokinase correlated significantly with serum insulin levels. The glucose-6-phosphate phosphohydrolase activity was unchanged or slightly lowered in the obese rats. The activity of malic enzyme was elevated in the obese animals.

Enhanced phosphoinositol hydrolysis in response to vasopressin in the septum of the homozygous Brattleboro rat

Arginine8-vasopressin (AVP) receptors in the septum of the Long-Evans rat have been shown to be both pharmacologically (displacement profiles) and functionally (ability to stimulate phosphoinositide hydrolysis) similar to the peripheral V1-type receptor for AVP. Previous binding studies of AVP receptors in the septum of heterozygous (HE) and homozygous (vasopressin-deficient, HO) Brattleboro (BB) rats revealed an increased number of receptors with a lower affinity for AVP in the HO-BB rat when compared to the HE-BB rat. To determine the effect of these receptor changes in the HO-BB rat septum on the postreceptor response of the tissue to AVP, concentration-response relationships for AVP-stimulated phosphoinositide hydrolysis were examined in septal slices from age-matched, adult male HE- and HO-BB rats. AVP-stimulated accumulation of [3H]inositol-1-phosphate (IP1) was significantly greater in the HO-BB (43.7%) than in the HE-BB (13.7%) at AVP concentrations of 10(-08) to 10(-05) M. The two groups did not, however, differ in their ability to stimulate [3H]IP1 accumulation in response to 2.0 mM carbachol. When the AVP-stimulated phosphoinositide response in both genotypes was compared to that obtained for the Long-Evans (LE) rat (the parent strain of the Brattleboro rat) septum under the same assay condition, it was found that the response in the HE-BB was much lower than in the LE. AVP receptor binding capacity (Bmax) correlated (r = 0.975) with release of IP1 ([3H]IP1 accumulation) for all 3 groups studied (LE, HE, HO).(ABSTRACT TRUNCATED AT 250 WORDS)

Dysregulation of glucose transport and transporters in perfused hearts of genetically obese (fa/fa) rats

The regulation of glucose transport in normal and insulin-resistant obese rat hearts have been studied by measuring glucose transport via the efflux of labelled 3-0-methyl-D-glucose. Glucose transporters in obese rat hearts were also investigated using the labelled cytochalasin B-binding assay. Basal, and insulin- or increasing workload-induced stimulation of glucose transport was decreased in obese rat hearts compared to those of normal ones. Total number of glucose transporters (plasma membrane plus microsomal ones) was about half that previously reported for normal rat hearts. Insulin or workload favoured the translocation of glucose transporters from an intercellular pool (microsomes) to the plasma membrane, as they do in normal rats. Due to the measured decrease in total number of transporters of obese rat hearts, those present in the plasma membrane (under basal conditions, or following stimulation by insulin or workload) were less than those previously found in normal rat hearts tested under identical conditions. In obese rat hearts, regulation of plasma membrane transporters was perturbed. The Hill coefficient (an index of positive cooperativity amongst glucose transporters) was paradoxically decreased by insulin while leaving affinity values unaltered. The Hill coefficient was unaltered by workload, although the affinity values were increased compared to respective controls. To sum up, obese rat hearts have decreased total transporter number, and although the two stimuli studied favour the translocation of available transporters, they fail to "activate" them adequately once present in the plasma membrane.

Ontogeny of vasopressin and oxytocin binding sites in the brain of Wistar and Brattleboro rats as demonstrated by lightmicroscopical autoradiography

Vasopressin (VP) and oxytocin (OT) binding sites were localized and quantified in the developing brain of the Wistar, heterozygous (Het) and homozygous (Hom) VP-deficient Brattleboro rat using an autoradiographical technique. VP binding sites could be demonstrated from prenatal day 20 onwards in the septum and in the lateral reticular nucleus. Between this and postnatal day 15, VP binding sites appeared in all other brain areas known to contain VP binding sites in adulthood. In the caudate putamen the regional distribution of VP binding changed during development, while in some areas, for instance, the dorsal hippocampus and post cingulate cortex, the concentration of binding sites increased early but decreased with age. Comparison of VP binding between Het and Hom rats showed significant differences in the lateral reticular nucleus during development. Moreover, at postnatal day 15 there was more VP binding in the anterior commissural and suprachiasmatic nucleus and less in the central amygdala, dorsal hippocampus and post cingulate cortex of the Hom rat. This study shows, for the first time, OT binding sites in the developing rat brain. There is a considerable overlap with VP binding in the brain, sometimes with the same developmental pattern, e.g. in the anterior olfactory nucleus and caudate putamen and sometimes with a later appearance, e.g. in the central amygdala and thalamic nuclei. However most areas with VP binding sites did not show OT binding. In some areas only OT binding sites were present, for instance in the islands of Calleja and ventromedial hypothalamus. Similar to some areas with VP binding, OT binding decreased between postnatal day 5 and 15 in the dorsal hippocampus and even completely disappeared in the parietal cortex. The existence of VP binding sites in the Hom rat, together with the only occasional relationship between the previously described ontogeny of VP and OT innervation of the brain and the presently described developmental course of binding sites, indicates that the early expression of binding sites is not initiated by endogenous ligand. However, the setting of the number of VP binding sites has probably been affected by the VP deficiency of the Hom Brattleboro rat.

Modulation of hypothalamic cholecystokinin receptor density with changes in magnocellular activity: a quantitative autoradiographic study

A combination of autoradiographical techniques and computerized image analysis has been used to study the distribution and density of cholecystokinin receptors in the paraventricular and supraoptic nuclei of animals in which the magnocellular-posterior pituitary axis is activated, namely, in salt-loaded (2% sodium chloride) and homozygous Brattleboro rats. [125I]cholecystokinin octapeptide binding was greatly elevated in the paraventricular, supraoptic and accessory nuclei of salt-loaded and homozygous Brattleboro rats, compared to the respective control animals. Furthermore, under these conditions [125I]cholecystokinin octapeptide binding in the paraventricular nucleus was localized almost exclusively to magnocellular subdivisions, and especially to those containing predominantly oxytocin neurons. Autoradiographical competition studies revealed that the increase in [125I]cholecystokinin octapeptide binding in magnocellular nuclei reflected an increase in receptor number (Bmax) rather than affinity (Kd). These results suggest that cholecystokinin receptor density in the paraventricular, supraoptic and accessory magnocellular nuclei is closely linked to magnocellular neurosecretory activity and raises the possibility that cholecystokinin receptors may be involved in oxytocin and vasopressin release processes.

Pharmacokinetic characteristics of the obese overfed rat

The present study was undertaken to examine the appropriateness of the obese overfed rat and the obese Zucker rat as animal models for evaluating drug disposition changes in human obesity. It was found that 11 of 12 characteristics that control or influence drug clearance and volume of drug distribution in obese humans were qualitatively reproduced in the obese overfed rat. In contrast, existing literature shows that the obese Zucker rat resembles the obese human in only five of 12 characteristics, with meaningful discrepancies in fat-free mass, creatinine clearance, and thyroid function. Perhaps of greatest significance were changes in hepatic cytochrome P-450, which increased in proportion to total body mass in the obese overfed rat but remain unchanged in the Zucker rat. Although P-450 status in human obesity is unknown, the overfed rat model provides an opportunity for examining increased oxidative drug elimination that appears as an established feature of human obesity. In conclusion, the obese overfed rat appears to be superior to the obese Zucker rat as an animal model for evaluating the pharmacological consequences of human obesity, particularly those in which reproducing drug pharmacokinetics is an important consideration.

Effect of food deprivation on regional brain glucose utilization in lean and fatty Zucker rats

Regional brain glucose utilization was investigated in lean and fatty Zucker rats when feeding status was changed. Ad-lib-fed fat rats exhibited lower glucose utilization in the central amygdala than ad-lib-fed lean rats. Food deprivation for 72 h enhanced glucose utilization in the ventromedial hypothalamus, lateral hypothalamic area of both phenotypes, hippocampus of fat rats, mammillary body and ventral tegmental area of leans. These results suggest association of the central amygdala with the development of genetic obesity and of the latter 5 areas with hunger-motivated behaviors.

The vasopressin precursor in the Brattleboro (di/di) rat

The vasopressin precursor in the rat hypothalamus has been studied, using trypsin to release desglycinamide vasopressin and coupling it to glycinamide (T & G treatment). The resulting amidated nonapeptide was detected and measured with a radioimmunoassay for vasopressin. The "vasopressin" produced in this way had the full immunoreactivity of the authentic peptide but eluted from an hplc column 1 min earlier and appeared to have a larger molecular weight. It was found that T&G treatment generated vasopressin immunoreactivity in extracts of the supraoptic nucleus (SON) of the Brattleboro rat in just the same way as it did in normal animals. Furthermore, this procedure produced vasopressin immunoreactivity in those hplc fractions from Brattleboro SON extracts that corresponded with the elution time of vasopressin precursor. Similar amounts of "vasopressin" could be generated from Brattleboro and normal SONs. These results support the suggestion that the Brattleboro SON synthesizes an aberrant vasopressin precursor which is not processed by the cell.

Developmental expression of neural cell type-specific mRNA markers in the myelin-deficient mutant rat brain: inhibition of oligodendrocyte differentiation

We have studied gene expression of neuroglial cell markers in the myelin-deficient (md) rat brain during postnatal development. Northern blots and slot blots of poly(A)+ RNA from developing brain were sequentially probed with cDNAs specific for the oligodendrocyte markers glycerol phosphate dehydrogenase (GPDH), myelin basic protein (MBP), and proteolipid protein (PLP), for the neuronal marker glutamic acid decarboxylase (GAD), and for the astrocyte markers glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS). GPDH mRNA levels were also examined in two peripheral tissues, liver, and skeletal muscle (hindlimb). Despite a lack of CNS myelin in the md mutant, transcripts of all oligodendroglial markers were detectable except the 1.6-kb PLP message. Brain GPDH mRNA levels were initially equivalent in md and unaffected littermates at postnatal day 15 (PI5), but the mutants failed to display the normal developmental increase in gene expression. By P25, GPDH mRNA expression in md rat brain was approximately 20% of control levels. GPDH mRNA expression in peripheral tissues was less affected than in brain and was lower in md mutants only at the later developmental ages. Expressions of GAD, GFAP, and GS mRNAs in developing md rat brain were not altered. The mRNA levels of the two myelin markers, MBP and PLP, were severely impaired in md rat brain during the entire myelinating period and represented less than 10% of control mRNA levels at P25. The most important observation was that the large PLP transcript (3.2 kb) was slightly shorter in size in md rat brain as compared to normals.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth hormone-deficient dwarfism in the rat: a new mutation

Mutations in animals have provided insight into many aspects of normal and pathological human physiology. This paper reports the discovery and initial characterization of a new mutant dwarf rat. The mutation, inherited as an autosomal recessive, arose spontaneously in a breeding colony of Lewis rats at the Medical Research Council Cellular Immunology Unit, Sir William Dunn School of Pathology, Oxford, U.K., in 1985 and the strain has now been established both in Oxford and at Mill Hill. Body growth in the mutant is retarded such that at 3 months of age both males and females weigh approximately 40% less than their normal litter-mates, and continue to grow at a slower rate. The mutants show a selective reduction in pituitary GH synthesis and storage (pituitary GH concentrations were approximately 10% of normal in males and 6% in females). The concentration of their anterior pituitary trophic hormones (LH, TSH, prolactin and ACTH) were within the normal range in dwarf animals. Exogenous GH treatment for 5 days resulted in an increase in growth rate from 1.5 +/- 0.3 to 3.9 +/- 0.4 g/day in male mutants, and 0.8 +/- 0.2 to 3.1 +/- 0.1 g/day in females. Longitudinal bone growth rates were more than doubled by this treatment from 49 +/- 5 to 100 +/- 10 micron/day in females and from 52 +/- 11 to 131 +/- 16 micron/day in males. Dot blot and Northern blot analysis of pituitary mRNA extracts revealed that the GH message in mutants was between 20 and 25% of normal, and that the GH transcript was of normal size.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential expression of vasopressin alleles in the Brattleboro heterozygote

A solution hybridization/RNase protection assay for the molar quantitation of vasopressin and oxytocin mRNAs, using synthetic complementary RNA probes, is described. This assay was optimized to permit the identification of vasopressin (AVP) mRNAs containing the frame-shift point deletion causing inheritable diabetes insipidus in the Brattleboro strain of rat. Examination of RNA from hypothalamic magnocellular tissue punches found that of the 86.1 x 10(-18) mol [86.1 attomoles (amol)] of AVP mRNA detected in the Brattleboro heterozygote paraventricular (PVN) nucleus, 5.2% could be shown to be mutant AVP mRNA (AVPd RNA). The percentage of AVPd RNA increased dramatically to 18.1% after 6 d of chronic intermittent salt-loading. Similar percentages and percentage increases of AVPd RNA were detected in the heterozygote supraoptic nucleus (SON). These values were contrasted with those found in parallel studies in both Long Evans and Brattleboro homozygotes, and compared with values for oxytocin (OT) mRNA in all 3 AVP rat genotypes. The results of continued osmotic regulation of the mutant AVP gene, the low native levels of AVPd RNA found in both the Brattleboro heterozygote and homozygote, and the magnitudes of AVPd expression change with chronic osmotic challenge were interpreted as indicating that (1) in the diploid rat genome, both AVP alleles are transcribed, (2) the osmotic regulation of the mutant AVP gene is normal, and (3) the low levels of AVPd mRNA are consistent with a shorter-than-control effective mRNA half-life.

Regulation of hypothalamic magnocellular neuropeptides and their mRNAs in the Brattleboro rat: coordinate responses to further osmotic challenge

A paradigm was developed for the chronic osmotic stimulation of homozygous diabetes insipidus rats of the Brattleboro strain, a strain that fails to synthesize vasopressin. This study examines the adaptation of 2 sets of coexisting peptide hormone magnocellular neurons in the hypothalamoneurohypophyseal system (HNS) of Long Evans (LE), Brattleboro heterozygote (HZ), and Brattleboro homozygote (DI) rats: (1) the arginine8-vasopressin (AVP)/dynorphin (DYN) neurons, and (2) the oxytocin (OT)/cholecystokinin (CCK8) neurons of the paraventricular and supraoptic nuclei, which project to the posterior pituitary. The regimen of chronic intermittent salt-loading (CISL) involved the replacement of 2% saline for normal drinking water for 18 hr/d. This protocol effectively increased plasma levels of AVP and OT in LE and HZ rats, oxytocin in DI rats, and maintained the posterior pituitary in a state depleted of AVP, OT, CCK, and peptides derived from pro-dynorphin: DYN A 1-17, DYN A 1-8, and DYN B 1-13. The ratio of pituitary DYN A 1-17 to DYN A 1-8 content in DI rats or in LE, HZ, and DI rats following 6 d of CISL suggests a preferential release of DYN A 1-17 during periods of chronic secretory activity. In response to chronic secretory activity, mRNAs for AVP, OT, DYN, and CCK increased 1.5-2-fold in all 3 AVP rat strains, with mRNAs for coexisting peptide hormones displaying parallel increases. Mutant AVP mRNA in the DI rat was expressed at very low levels and DYN mRNA in very high levels, with each of these mRNAs continuing to be regulated by CISL in a normal manner. These results suggest a regulatory relationship between AVP and OT neurons, in which vasopressin neurons are feedback-regulated by AVP, most likely via plasma osmolarity, and that oxytocin neurons are modulated by peptides derived from pro-dynorphin.

Twenty-four-hour pineal melatonin synthesis in the vasopressin-deficient Brattleboro rat

The diurnal time course of pineal melatonin synthesis was analyzed simultaneously in the arginine vasopressin (AVP)-deficient Brattleboro rat (BB), the Long-Evans (LE) and Sprague-Dawley (SD) rat by means of radioenzymatic determination of the rate-limiting enzyme serotonin-N-acetyltransferase (NAT) and the melatonin content over a period of 24 h. While all 3 strains displayed a distinct day-night rhythm of melatonin synthesis (low day-time, high night-time values), BB rats generally exhibited lower NAT values as compared to LE and SD rats, though reaching a significant difference at 02.99 h only. Twenty-four-hour melatonin content was characterized by distinct nocturnal maxima in LE and SD rats, while BB rats showed a plateau-like nocturnal time course. Electrophysiological and pharmacological findings in SD rats point to an inhibitory influence of AVP upon pineal melatonin synthesis. The lack of AVP obviously does not result in disinhibition of pineal melatonin synthesis but rather in a different time course of pineal melatonin content. This might either be due to strain differences or to yet unknown compensatory mechanisms in BB rats.